tm.asm

利用DOS提供的中断调用功能和BIOS系统调用功能

code  segment      
          assume  cs:code,ds:code  
org  100h  
          start:   jmp  install  
          msg          db  'Current time is:  '  
          time0      db  ?,?  
                      db  ':'  
          time1      db  ?,?    
                      db  ':'  
          time2      db  ?,?,0,0  
oldint1c             dd  ?  
newint1c:  push  ax  
                  push  bx  
                  push  cx  
                  push  dx  
                  push  si  
                  push  di  
                  push  es 
                  mov  ax,0200h  
                  int  1ah  
                  mov  al,ch 
                  lea  si,time0  
                  call  bcd  
                  mov  al,cl  
                  lea  si,time1  
                  call  bcd  
                  mov  al,dh  
                  lea  si,time2  
                  call  bcd 
                 mov  ax,0b800h  
                  mov  es,ax  
                  mov  di,54*2d  
                  lea  si,msg  
      disp:  mov  al,cs:[si]  
                  inc  si  
                  or  al,al 
                  jz  disp0  
                  cld   
                  stosb  
                  inc  di 
                  jmp  disp  
disp0:            pop  es  
                  pop  di  
                  pop  si  
                  pop  dx  
                  pop  cx  
                  pop  bx  
                  pop  ax  
                  jmp  cs:oldint1c 
      bcd:    mov  ah,al 
                  shr  ah,1  
                  shr  ah,1  
                  shr  ah,1  
                  shr  ah,1  
                  and  al,0fh  
                  add  ax,'00'  
                  xchg  ah,al  
                  mov  cs:[si],ax  
                  ret  
install:    push  cs  
                  pop  ds  
                  mov  ax,351ch  
                  int  21h  
                  mov  word  ptr  oldint1c,bx  
                  mov  word  ptr  oldint1c+2,es  
                  lea  dx,newint1c 
                  mov  ax,251ch  
                  int  21h  
                 mov  dx,offset  install+120h   
                  mov  cl,04h  
                  shr  dx,cl 
                  mov  ah,31h  
                  int  21h  
code  ends  
end  start